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What is meant by base exposure? (3 replies and 4 comments)

xpialidocious
1 month ago
xpialidocious 1 month ago

What is meant by base exposure? 

 

I'm looking over a DP's (Rina Yang) tech breakdown for a project, and her setups are written in this similar format: 35mm 500T RATED at 320ASA - NEED T4-5.6 (of course, her other setups have varying T-Stop requirements).

Is the T-Stop range her base exposure? As I understand it, certainly the entire space isn't reading in this range, because the contrast levels are variant, and it'd be a flat scene otherwise. So where in the scene is she reading for (T4-5.6)? 

When a DP says they want base exposure at a particular range, particularly when shooting film, where in the scene is should this be read from? Is it the general ambience? and how? with an incident reading in the middle of the scene? Would one hold up a grey card in the middle of the scene, and spot meter it? 

 

Thanks!

Frank
1 month ago
Frank 1 month ago

My understanding is that base exposure usually is relative to 18% grey

xpialidocious
1 month ago
xpialidocious 1 month ago

Update: I did some more reading. So from what I understood, the T-Stop range is what you'd want "at key" correct? So if you incident read your scene (which would give you the same reading as if you spot read, a 18% gray card in that same position from the camera, correct?), at around where the subject would be placed you're wanting it to fall between T4-T5.6 (from the example). From there you adjust the other lights to achieve your desired ratio? Is this on the right track? 

 

Base exposure is for "at-key" not necessarily the foot-candles, or general ambient light?

xpialidocious
1 month ago

I think I'm understading where I was confused. Somewhere along the line I began to believe a DP needing a certain T-Stop, was meaning them needing a minimum level of ambient in a scene before placing lights, especially when it comes to a set ASA such as when your'e shooting film.

dmullenasc
1 month ago
dmullenasc 1 month ago

It's a vague word, "base" exposure. If by "ambience" you mean general fill levels, no, that's not the meaning of base exposure unless the soft ambient light was the key light.

I think one usually says "base exposure" as in general planned exposure for the scene, so it's probably referring to the main light source for the action of the scene.

Now perhaps one DP will tell a gaffer to get an f/2.8 "base" but plan on shooting at f/4 for a slight underexposed look... so in that case, it's not the planned exposure for the scene but instead the "base" exposure is if the main light source was exposed normally. Like I said, it's a vague word. It's more of a target to aim for.

dmullenasc
1 month ago

I think in the example originally mentioned, "need T/4.5-5.6" means that is the intended shooting stop at the widest (could even mean she was working with a 10:1 anamorphic zoom lens which are often T/4.5 at the widest.)

dmullenasc
1 month ago

So if your lens could only open to T/4.5 at the widest and that was your shooting stop, it doesn't mean that the key levels were lit to T/4.5 necessarily, one could have a scene in a darker restaurant where the faces read T/2.8 on the meter but the scene was shot at T/4.5 so that the faces were 1.5-stops under.

xpialidocious
1 month ago

Yes! Thank you dmullenasc. This was a great explanation and I appreciate the nuance in your example.

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